The present invention disclosed herein relates to a chemical compound being used for forming a random wrinkle structure, composition containing the compound, film having the structure, method of forming the film, and OLED comprising the film.
Films having a random wrinkle structure may be used in various fields. For example, such a structure may be used in an organic light emitting diode (OLED).
An organic light emitting diode is a self-luminous type device which emits light by electrically exciting an organic light emitting material. The organic light emitting diode includes a substrate, an anode, a cathode, and an organic light emitting layer formed between the anode and the cathode. Holes and electrons supplied from the anode and the cathode are combined in the organic light emitting layer to generate externally emitted light.
The organic light emitting diode is a device which is formed by physically stacking various elements such as a substrate, an organic layer, and a metal thin film. The light generated in the organic light emitting layer becomes visible light after passing through an interface between heterogeneous materials and films having different refractive indices. The light generated due to the interface and the different refractive indices may be guided or may be undergone a total reflection process. As a result, loss of about 80% of the light occurs in an OLED having a typical thin film stack structure and only about 20% of the light is emitted from the OLED device and obtained as visible light. An increase in applied voltage is inevitably required in order to secure above a predetermined level of brightness. The applied voltage results in negative consequence for the device broadly in terms of two aspects. First, energy consumption increases due to the increase in the applied voltage. Second, deterioration of the organic layer progresses in the case that the organic layer is continuously exposed in a high voltage and thus, lifetime of the device decreases. Therefore, there is a need for a technique that is able to effectively extract the generated light for the purpose of energy saving and longer lifetime. Technical approach performed to increase extraction efficiency of the generated light is commonly denoted as light extraction technology. The light extraction technology is generally classified as internal light extraction technology and external light extraction technology. A portion of the generated light becomes trapped due to the difference between refractive indices of the transparent anode and the substrate, and disappears by being guided between the anode and the substrate. In order to extract the light disappeared as above, there is a method of patterning irregular unevenness in a substrate for the possible light scattering in the substrate and the method is denoted as internal light extraction. The light entered into the substrate by the internal light extraction method may not escape from the inside of the substrate to an air layer due to the difference between refractive indices of the substrate and the air layer as described above, and thus, may disappear by being guided in the substrate. In order to extract the light disappeared as above to the outside of the air layer, a film or the like having unevenness etched therein is attached to an opposite side of the patterned unevenness and this is denoted as external light extraction. A film generally used for the external light extraction is a microlens array (MLA) film. With respect to the microlens array film, regularly patterned microlenses are formed on a film by using an imprinting method using an ultraviolet (UV)-curable material or an embossing method using a thermoplastic film. A block copolymer is used as a method of increasing light extraction by simply forming a random wrinkle structure on a film. The random wrinkle structure may be formed on a surface of the film by using a simple process employing the block copolymer, but depth and width of the random wrinkle structure may be relatively small, and thus, visible light may not be efficiently extracted.